On Debian there are (at least) two convenient ways of installing stuff.
1) If you want just a newer package, and you do NOT want to apply your own patch, your own configure options, etc.
Use APT-Pinning. It can grab packages and dependencies (only those), from testing/sid/experimental. And it won't mess your system up.
https://wiki.debian.org/AptPreferences
http://jaqque.sbih.org/kplug/apt-pinning.html
2) If you want to apply your own patch, or the apt-pinning method does not work for you, you can use `pbuilder`.
It is a tool that will grab all the dependencies, install them into a virtual environment, and create the package.
And nothing will happen on your physical machine (e.g.: It remains untouched), except you will have your package built.
https://wiki.ubuntu.com/PbuilderHowto
You can download Debian source packages with dget.
> su
> $ apt-get install debian-goodies
then you go up to the debian online repository and open a package, such as
http://packages.debian.org/sid/qbittorrent
There will be a .dsc file there.
Copy link, and use a terminal:
dget -x -u
http://ftp.de.debian.org/debian/pool/ma ... .9.8-1.dsc
It will download every patch, debian file, and the source. Even unpack it for you.
After this, give it to pbuilder and you are done.
It may sound complicated but once you learn it, it's real easy. (And well, you use Linux, you should know your OS.)
(***) = The compile consists of basically three basic steps.
0 _optional_) Apply any patches you need, want.
1) ./configure --with-what-you-want --prefix=/usr
(implying you want to put it under /usr... that's the default, though. but if you install it there, it will overwrite your current install!)
2) make
3) sudo make install
(Only the last needs root permissions.)
